1. Field of the Invention
The present invention relates to a code error correcting device for decoding a code train which is obtained by error correction encoding digital information such as digital image information having a correlation by a chain-like encoding construction.
2. Related Background Art
Generally, a system for digitizing an information signal such as image information or the like and transmitting (recording) uses a method whereby the information signal is converted into a transmission code adapted to a transmission medium and transmitted. At this time, in many cases, input data is compressed and encoded due to a limitation of a transmission bit rate. On the other hand, as a countermeasure for the occurrence of transmission errors, an error correction code is added.
FIGS. 1A and 1B are schematic constructional block diagrams of a conventional digital information transmission system. FIG. 1A shows a transmitting system (recording system) and FIG. 1B shows a receiving system (reproducing system). In the transmitting system (recording system), a compression encoding circuit 10 compresses and encodes an information signal such as digital image information or the like by using its correlation. An output of the compression encoding circuit 10 is supplied to an error correction encoding circuit 12, by which an error correction encoding is executed as a counter-measure for transmission errors. A modulation circuit 14 modulates an output of the error correction encoding circuit 12 into a format adapted to characteristics of a transmission path and outputs it to the transmission path (records onto a recording medium).
On the other hand, in the receiving system (reproducing system), a demodulation circuit 16 demodulates the transmission signal of the transmission path. An error correction decoding circuit 18 corrects errors generated on the transmission path. An expansion circuit 20 executes expanding and reconstructing processes opposite to the processes of the compression encoding circuit 10. For data which is determined by the error correction decoding circuit 18 to be uncorrectable, error modification such as data substitution or the like is executed by an error modification circuit 22.
However, in the conventional example as mentioned above, in the case of executing the modifying operation in the error modification circuit 22, information to be modified must be determined on the basis of a compressing method by referring to a correction flag from the error correction decoding circuit 18. As mentioned above, error uncorrectable information cannot be merely discriminated by only the correction flag. A circuit to determine the information to be modified is inevitable as mentioned above. It is difficult to realize a high processing speed and to simplify a circuit construction.